Nvis compatible backlight device and lcd using the same

ABSTRACT

Exemplary embodiments provide an electronic display assembly comprising a liquid crystal layer and a light guide positioned behind the liquid crystal layer. The light guide preferably includes a light emission surface and a light-collecting portion opposing the light emission surface. A pair of opposing side portions may define the periphery of the light guide. A first plurality of LEDs are placed so as to direct the emitted light into the light-collecting portion. An NVIS filter is preferably placed adjacent to at least one of the side portions. A second plurality of LEDs are placed to direct the emitted light through the NVIS filter and into a side portion of the light guide. Alternative embodiments can contain directing elements to direct the light from the second plurality of LEDs into the edge portions of the light guide.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S.application Ser. No. 13/937,756, filed on Jul. 9, 2013. U.S. applicationSer. No. 13/937,756 is a continuation of U.S. application Ser. No.12/897,829, filed on Oct. 5, 2010, now U.S. Pat. No. 8,480,281 issuedJul. 9, 2013, which is a non-provisional application of U.S. ApplicationNo. 61/248,870 filed on Oct. 5, 2009. All aforementioned applicationsare hereby incorporated by reference herein as though re-written in itsentirety.

FIELD OF THE EXEMPLARY EMBODIMENTS

The exemplary embodiments are directed generally towards backlightdevices for liquid crystal displays (LCDs) used in conjunction withnight vision imaging systems.

BACKGROUND OF THE GENERAL INVENTIVE CONCEPT

In the past, LCDs have been used in a wide variety of environments,including displays within the cockpit of an aircraft as well asground-based vehicles. In some of these environments it is desirable tohave LCDs with dual mode backlighting. These displays have one mode foruse during daylight operation and a second mode for nighttime operationwhen an observer may be using a night vision imaging system, hereafter‘NVIS.’ It has been known to use filtered light during the NVIS mode astypical night vision components are sensitive to light within a certainwave length range. Filtering the light allows the LCD to be usedsimultaneously with NVIS equipment. For example, MIL-STD-3009 (UnitedStates Department of Defense Interface Standard Lighting, Aircraft,Night Vision Imaging System (NVIS) Compatible) specifies the smallamount of light (at wavelengths longer than ˜650 nm) which may beemitted by an NVIS-compatible display. The disclosure of MIL-STD-3009 isherein incorporated by reference in its entirety. Without other changes,the filtering which helps NVIS performance would degrade the opticalperformance (mainly color and brightness) of the same LCD when used indaylight operations.

LCDs require a backlight in order to produce an image as these devicesdo not produce light themselves. Previous devices have used backlightswith two sets of light emitting diodes (LEDs): one set for daylight anda second set for nighttime. The set of LEDs which are used duringnighttime operations are typically covered by an NVIS filter (sometimescalled ‘hot mirror’ filters) which absorb or reflect electromagneticradiation within a certain wavelength. Some displays which use directbacklighting techniques for the nighttime operations may place a smallNVIS filter over each LED. With some displays containing hundreds (orthousands) of LEDs, the manufacturing costs for producing and assemblingthe many small filters can be very high. Other displays may filter allof the LEDs (even the daytime LEDs) which typically results in reducedcolor gamut and brightness for the display.

Further, the light uniformity of the backlight is often important anddesirable. Because LEDs are point sources of light, it is typicallyimportant that their natural illumination is modified to produce auniform level of illumination across the LCD screen. Light-diffusing(and sometimes scattering) devices have been commonly used for thispurpose. However, when used in a direct-lit fashion (as opposed toedge-lit) there must be a space between the LEDs and the diffusingdevices (known sometimes as a ‘throw distance’) which forces the entireLCD assembly to become thicker. To further increase the light uniformityof the backlight, a large number of low-power LEDs is typically moredesirable than a small number of high-power LEDs. Not only does thisincrease the light uniformity, but low-power LEDs are typically moreefficient than high-power LEDs. Thus, the use of many low-power LEDs canresult in power savings as well as smaller amounts of heat generation.

However, as mentioned above, using more LEDs for nighttime operation mayincrease the manufacturing costs by adding more filters and assemblytime to install the filters. This problem is especially troublesome forthe nighttime LEDs because the human eye's sensitivity to lightvariation is much more noticeable at low levels (dim) rather than highlevels (bright). Thus, it is very desirable to maximize the uniformityof the light emanating from the nighttime LEDs. Further, it is alsodesirable to produce the brightest possible daytime LCD with the highestpossible contrast ratio while also minimizing the thickness of the LCDassembly and its overall energy consumption.

SUMMARY OF THE EXEMPLARY EMBODIMENTS

An exemplary embodiment uses a hybrid backlight assembly which uses acombination of direct and edge lighting technology to obtain the optimumperformance for the overall LCD assembly. For the daytime operations, amodular direct backlight setup is used where the traditional lightdiffusing/scattering sheet has been removed and the throw distance hasbeen largely decreased. A specialized light guide provides a scatteringand diffusing effect where the light guide can be placed closer to theLCD stack, providing a very thin overall assembly. Because of the directlighting setup, the daytime LEDs can produce a high level of luminanceand can also be controlled for dynamic localized dimming of certainareas of the backlight. The localized dimming capability allows sectionsof the backlight to be ‘dimmed’ or have their respective illuminationlevels decreased when it is not necessary. This saves power, improvesthe contrast ratio, and reduces the amount of heat that the backlightgenerates.

For the nighttime operations, low power LEDs may be oriented in anedge-lit fashion along at least one edge of the specialized light guide.A substantially continuous hot mirror filter may be placed along thelight guide as well, between the nighttime LEDs and the light guide. TheLEDs may be somewhat densely spaced so as to maximize the uniformity ofthe NVIS compatible light. In some embodiments, there may be an array ofnighttime LEDs placed on two opposing edges of the display. By using lowpower LEDs, the power density is distributed more evenly and thebacklight can provide a more efficient light source.

Alternative embodiments may place the daytime LEDs in a traditionaldirect-lit fashion with the nighttime LEDs placed in an edge-lit fashionwith a more traditional light guide. In some embodiments, both thedaytime LEDs and the nighttime LEDs can be mounted onto a single printedcircuit board (PCB) assembly. This can greatly reduce assembly times andmanufacturing costs.

Overall, the LCD assembly can be thinner, lighter, and cheaper tomanufacture. The luminance uniformity is superior (especially with theNVIS LEDs) and the daytime operations provide a high contrast ratio,high luminance, lower power consumption, and lower heat generation.These features are important especially with aircraft and groundvehicles where weight and power consumption are often important designconstraints.

BRIEF DESCRIPTION OF THE DRAWINGS

In addition to the features mentioned above, other aspects of the willbe readily apparent from the following descriptions of the drawings andexemplary embodiments, wherein like reference numerals across theseveral views refer to identical or equivalent features, and wherein:

FIG. 1A is a bottom perspective view of an exemplary embodiment of thebacklight device;

FIG. 1B is a bottom perspective view of an alternative embodiment of thebacklight device;

FIG. 1C is a bottom perspective view of an alternative embodiment of thebacklight device;

FIG. 2 is a planar bottom view of the embodiment from FIG. 1;

FIG. 3 is a planar side view of an exemplary embodiment of a liquidcrystal display using the embodiment of the backlight device from FIGS.1 and 2;

FIG. 4A is a side planar view of Detail 4 from FIG. 3;

FIG. 4B is a side planar view of an alternative embodiment for Detail 4from FIG. 3;

FIG. 5A is a top perspective view of another embodiment for thebacklight device;

FIG. 5B is a bottom perspective view of the embodiment of the backlightdevice from FIG. 5A;

FIG. 6 is a planar bottom view of the embodiment from FIGS. 5A and 5B;

FIG. 7 is a planar side view of an exemplary embodiment of a liquidcrystal display using the embodiment of the backlight device from FIGS.5A, 5B, and 6;

FIG. 8 is a sectional view along section line 8-8 indicated in FIG. 7;and

FIG. 9 is a perspective sectional view of another embodiment of thebacklight device used in a liquid crystal display.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S)

Herein, the terms ‘vertical’ and ‘horizontal’ will be used to describethe relative orientation of different elements. Thus, as used herein,‘horizontal’ means substantially parallel to the associated liquidcrystal stack. Also, as used herein, ‘vertical’ means substantiallynormal to the associated liquid crystal stack.

FIG. 1A is a bottom perspective view of one embodiment of the backlightdevice 100. An exemplary light guide 30 would preferably consist ofseveral surfaces. A light collecting surface 31 is adapted to collectlight from a first plurality of LEDs 20. A light emission surface 32 mayoppose the light collecting surface 31 and is adapted to emit light intothe liquid crystal display stack (or whatever component is placedbetween the backlight device 100 and the liquid crystal display stack).A first 33 and second 34 pair of opposing edge surfaces may be used todefine the general periphery of the light guide 30. A NVIS filter 65 maybe placed adjacent to at least one of the edge portions 34. A secondplurality of LEDs 55 are preferably arranged so that the light isemitted through the NVIS filter 65 and into the light guide 30. Someembodiments may also include a second NVIS filter 60 and a thirdplurality of LEDs 50 arranged so that the emitted light passes throughthe second NVIS filter 60 and into the light guide 30. The second NVISfilter 60 and third plurality of LEDs 50 are preferably placed on theedge surface which opposes the first NVIS filter 65 and second pluralityof LEDs 55, but this is not required.

FIG. 1B is a bottom perspective view of an alternative embodiment of thebacklight device 101. In this embodiment, NVIS filter 65 is placedadjacent to one of the edge portions 33. Again, a second plurality ofLEDs 55 are preferably arranged so that the light is emitted through theNVIS filter 65 and into the light guide 30. Some embodiments may alsoinclude a second NVIS filter 60 and a third plurality of LEDs 50arranged so that the emitted light passes through the second NVIS filter60 and into the light guide 30. In this particular embodiment, thesecond NVIS filter 60 and third plurality of LEDs 50 are placed adjacentto edge portion 33. The second NVIS filter 60 and third plurality ofLEDs 50 are preferably placed on the edge surface which opposes thefirst NVIS filter 65 and second plurality of LEDs 55, but this is notrequired.

FIG. 1C is a bottom perspective view of an alternative embodiment of thebacklight device 102. In this embodiment, NVIS filters and associatedLEDs are placed adjacent to the first 33 and second 34 pair of opposingedge surfaces, which may be used to define the general periphery of thelight guide 30. Similar to the embodiment of the backlight device 100 inFIG. 1A, a NVIS filter 65 and a second plurality of LEDs 55 may beplaced adjacent to at least one of the edge portions 34. Further, asecond NVIS filter 60 and a third plurality of LEDs 50 are arranged sothat the emitted light passes through the second NVIS filter 60 and intothe light guide 30. In addition, a third NVIS filter 65′ and fourthplurality of LEDs 55′ are placed adjacent to one of the opposing edgeportions 33. A fourth NVIS filter 60′ and fifth plurality of LEDs 50′ isalso placed adjacent to one of the opposing edge portions 33.

FIG. 2 is a planar bottom view of the embodiment of the backlight device100 from FIG. 1A. This figure illustrates the light 56 emitted from thesecond plurality of LEDs 55 which preferably passes through the NVISfilter 65 and into the light guide 30. Also shown in this figure is thelight 51 emitted from the optional third plurality of LEDs 50 whichpreferably passes through the NVIS filter 60 and into the light guide30.

FIG. 3 is a planar side view of an exemplary embodiment of a liquidcrystal display using the embodiment of the backlight device 100 fromFIGS. 1A and 2. Here, the basic components for a typical LCD are shown:a front polarizer 14, a liquid crystal stack 10, and a rear polarizer12. As well known in the art, LCD assemblies may contain a variety ofadditional layers such as antireflection layers (AR), additional linearor circular polarizers, phase retarders, light diffusing or scatteringlayers, alignment layers, heater layers, EMI shielding layers, etc. Thecomponents of a liquid crystal stack 10 are also well known in the artand can vary depending on the type of liquid crystal material being usedand its specific application. A typical liquid crystal stack 10 wouldcontain two transparent substrates (typically glass or plastic) withliquid crystal material sandwiched in between. An electrical controllingmechanism (sometimes an electrode or thin-film transistor) is typicallyused to apply an electrical potential to portions (pixels or sub-pixels)of the liquid crystal material. As the specifics of liquid crystalstacks 10 and other optical layers are not necessary for the exemplaryembodiments, they will not be discussed further herein. The exemplaryembodiments herein can be applied to any type of LCD assembly, which mayinclude more or less components than what is shown in the variousfigures.

This particular embodiment of the light collecting surface 31 of thelight guide 30 uses a ‘saw-tooth’ type of profile for the lightcollecting surface 31 which, in this embodiment is comprised ofalternating substantially vertical sub-surfaces 36 and slantedsub-surfaces 37. For the daytime operations of the display, the firstplurality of LEDs 20 (daytime) may be placed adjacent to the variousvertical sub-surfaces 36 of the light guide 30. These daytime LEDs 20may be mounted to a supporting structure 25 which may be a printedcircuit board (PCB). In an exemplary embodiment, the LEDs 20 would bemounted on a metal core PCB which has a low level of thermal resistancebetween the surface containing the LEDs 20 and the opposing surface. Thesurface of the supporting structure 25 which contains the LEDs 20 may bereflective so that light rays will be re-directed towards the lightguide 30 and only minimally absorbed. A ‘white’ surface may be used or areflective coating may be applied.

FIG. 3 also indicates the location of Detail 4 which is shown in FIGS.4A and 4B.

FIG. 4A is a side planar view of Detail 4 from FIG. 3. In thisembodiment, the light rays of the first plurality of LEDs 20 preferablyenter the light guide 30 primarily through the vertical sub-surfaces 36.Optionally, the vertical sub-surfaces 36 may scatter the light as itenters the light guide 30. Also optionally, the interior of the lightguide 30 can scatter the light once it enters the light guide 30. Onceinside the light guide 30, the light rays may interact with the slantedsub-surfaces 37 where it may be reflected towards the light emittingsurface 32 of the light guide 30. Optionally, the slanted sub-surfaces37 may also scatter the light while reflecting it towards the lightemitting surface 32.

For this embodiment, the light guide 30 can be described as having afirst 33 and second 34 pair of opposing edge surfaces which may be usedto define the periphery of the light guide. The first pair of opposingedge surfaces 33 may be parallel (or substantially parallel) with thesubstantially vertical sub-surfaces 36 of the saw-tooth light collectingsurface 31 of the light guide 30. Also in this embodiment, the secondpair of opposing edge surfaces 34 are generally orthogonal (or normal)to the substantially vertical sub-surfaces 36 and the first pair ofopposing edge surfaces 33. As shown in FIGS. 1-3, the second pluralityof LEDs 55 and optional third plurality of LEDs 50 are generallyoriented in an edge-lit fashion along at least one of the second pair ofopposing surfaces 34 which are generally orthogonal to the verticalsub-surfaces 36.

FIG. 4B is a side planar view of an alternative embodiment of Detail 4from FIG. 3. Similar to the previously described embodiment, the lightrays of the first plurality of LEDs 20′ preferably enter the light guide30′ primarily through the vertical sub-surfaces 36′. Optionally, thevertical sub-surfaces 36′ may scatter the light as it enters the lightguide 30′. Also optionally, the interior of the light guide 30′ canscatter the light once it enters the light guide 30′. Once inside thelight guide 30′, the light rays may interact with the slantedsub-surfaces 37′ where it may be reflected towards the light emittingsurface 32′ of the light guide 30′. Optionally, the slanted sub-surfaces37′ may also scatter the light while reflecting it towards the lightemitting surface 32′.

For this particular embodiment, the light collecting surface 31′contains an additional substantially horizontal sub-surface 38′ whichconnects the vertical sub-surface 36′ with the slanted sub-surface 37′.The addition of the horizontal sub-surface 38′ increases the surfacearea of the edge surface 34′ which is adjacent to the mounting structure25′ for the various LEDs. A NVIS filter 65′ may be placed between thesecond plurality of LEDs 55′ (here the night-mode LEDs) and at least aportion of the edge surface 34′ of the light guide 30′. This embodimentallows the second plurality of LEDs 55′ (here the night-mode LEDs) to beplaced directly adjacent to the saw-tooth profile (rather than above thesaw-tooth profile as shown in FIGS. 1A-3). Specifically in reference toFIG. 4B, the light emanating from the second plurality of LEDs 55′ wouldbe directed into the page (i.e. through the NVIS filter 65′ and into thelight guide 30). Thus, the second plurality of LEDs 55′ and the NVISfilter 65′ have been shown with solid lines while the sub-surfaces 36′,37′, and 38′ as well as the first plurality of LEDs 20′ are shown withhidden lines. In this embodiment, the first plurality of LEDs 20′ andthe second plurality of LEDs 55′ may be placed on the same mountingstructure 25′.

While FIGS. 1A-4B show the surfaces 33, 34, 36, and 37 as substantiallyflat surfaces, other embodiments may use a curved profile for surfaces33, 34, 36, and/or 37. Thus, these surfaces may be curved to perform alens-like functionality or perform other enhanced optical featuresincluding, but not limited to, collimation, steering, and/or diffusionof light.

FIG. 5A is a top perspective view of another embodiment for thebacklight device 200. FIG. 5B is a bottom perspective view of theembodiment of the backlight device 200 from FIG. 5A. FIG. 6 is a planarbottom view of the embodiment from FIGS. 5A and 5B.

A light collecting surface 131 is adapted to collect light from a firstplurality of LEDs 120. A light emission surface 132 may oppose the lightcollecting surface 131 and is adapted to emit light into the liquidcrystal display stack (or whatever component is placed between thebacklight device 200 and the liquid crystal display stack). A first 133and second 134 pair of opposing edge surfaces may be used to define theperiphery of the light guide 30. A NVIS filter 165 may be placedadjacent to at least one of the edge portions 134. A second plurality ofLEDs 155 are preferably arranged so that the light is emitted throughthe NVIS filter 165 and into the light guide 130. Some embodiments mayalso include a second NVIS filter 160 and a third plurality of LEDs 150arranged so that the emitted light passes through the second NVIS filter160 and into the light guide 130. The optional second NVIS filter 160and third plurality of LEDs 150 are preferably placed on the edgesurface which opposes the first NVIS filter 165 and second plurality ofLEDs 155, but this is not required.

FIG. 7 is a planar side view of an exemplary embodiment of a liquidcrystal display using the embodiment of the backlight device from FIGS.5A, 5B, and 6. The typical components for an LCD are shown: a frontpolarizer 14, a liquid crystal stack 10, and a rear polarizer 12. Asdiscussed above and well known in the art, LCD assemblies may contain avariety of additional layers. These are not necessary or critical to theexemplary embodiments herein though, and will not be discussed further.

Similar to the embodiments described above, the light collecting surface131 of the light guide 130 uses a ‘saw-tooth’ type of profile for thelight collecting surface 131 which, in this embodiment is comprised ofalternating substantially vertical sub-surfaces 136 and slantedsub-surfaces 137. For the daytime operations of the display, the firstplurality of LEDs 120 (daytime) may be placed adjacent to the variousvertical sub-surfaces 136 of the light guide 130. These daytime LEDs 120may be mounted to a supporting structure 125 which may be a printedcircuit board (PCB).

FIG. 8 is a sectional view along section line 8-8 which cuts through arow of the first plurality of LEDs 120 in FIG. 7. In this embodiment, asubstantially horizontal surface 166 extends outwardly from the lightcollecting surface 131 of the light guide 130. A slanted surface 167connects the horizontal surface 166 with the light emitting surface 132.A NVIS filter 165 is preferably placed adjacent to the substantiallyhorizontal surface 166. A second plurality of LEDs 155 (here night-modeLEDs) is preferably arranged below the horizontal surface 166 and NVISfilter 165 so that the emitted light primarily passes through the NVISfilter 165, horizontal surface 166, and reflects off slanted surface167.

If desired, a similar arrangement can be placed on the opposing edgesurface. Thus, a second substantially horizontal surface 161 couldextend outwardly from the light collecting surface 131 of the lightguide 130. A slanted surface 162 connects the horizontal surface 161with the light emitting surface 132. A NVIS filter 160 is preferablyplaced adjacent to the substantially horizontal surface 161. A thirdplurality of LEDs 150 (here night-mode LEDs) is preferably arrangedbelow the horizontal surface 161 and NVIS filter 160 so that the emittedlight primarily passes through the NVIS filter 160, horizontal surface161, and reflects off slanted surface 162.

It is preferable that slanted surfaces 162 and 167 are reflective. It ismore preferable that slanted surfaces 162 and 167 have highly reflectiveand scattering properties (techniques for these properties are discussedbelow). It may also be preferable to place a reflective surface 168between the second plurality of LEDs 155 and the light collectingsurface 130 (and/or vertical sub-surface 136) of the light guide 130 toprevent unfiltered electromagnetic radiation from entering the lightguide 130 (and ultimately the LCD). Similarly, it may also be preferableto place a reflective surface 163 between the third plurality of LEDs150 and the light collecting surface 130 (and/or vertical sub-surface136) of the light guide 130. In these embodiments, the reflectivesurfaces 168 and 163 may be oriented substantially vertically.

Optionally, the light guide 130 may be substantially rectangular inshape while the slanted reflective surfaces 162 and 167 are formed asseparate surfaces. There exists a very wide range of options for formingsurfaces 162 and 167, including but not limited to bulk metal, bulkglass, and pre-form plastics and metals. Those skilled in the art willenvision many possibilities for forming surfaces 162 and 167, with someapproaches having advantages over others in particular applications.Although shown in the figures as flat, further embodiments may provide acurved profile for surfaces 161, 162, 166 and 167. Thus, these surfacesmay be curved to perform a lens-like functionality or perform otherenhanced optical features including, but not limited to, collimation,steering, and/or diffusion of light.

It should be noted that although the NVIS filters and associated LEDsare shown along opposing edges 134, they could alternatively be placedalong opposing edges 133. Further, NVIS filters and associated LEDscould be placed along both opposing edges 134 and opposing edges 133 (soas to substantially surround the entire periphery of the light guide130).

FIG. 9 is a perspective sectional view of another embodiment of thebacklight device used in a liquid crystal display. A generally planarlight guide 430 may be used which contains a light collecting surface431 which is adapted to collect light from a first plurality of LEDs420. (The light guide 430 is not shown cross-hatched for clarity) Inthis embodiment, the first plurality of LEDs 420 are arranged in atraditional direct-lit fashion (i.e. oriented so that the axis of thestrongest portions of emitted light are oriented vertically or,perpendicular to the associated liquid crystal stack). A light emissionsurface 432 may oppose the light collecting surface 431 and is adaptedto emit light into the LCD components 480. Two pairs of opposing edgesurfaces may be used to define the periphery of the light guide 430.Since FIG. 9 is a partial section view, only one edge surface 434 isshown, but this edge could be any one of the opposing edge surfaces ofthe light guide 430. A NVIS filter 465 may be placed adjacent to atleast one of the edge surfaces (here its adjacent to edge surface 434).A second plurality of LEDs 455 are preferably arranged so that the lightis emitted through the NVIS filter 465 and into the light guide 430.Some embodiments may also include a second NVIS filter and a thirdplurality of LEDs arranged so that the emitted light passes through thesecond NVIS filter and into the light guide 430. The second NVIS filterand third plurality of LEDs would preferably be placed on the edgesurface which opposes the first NVIS filter 465 and second plurality ofLEDs 455, but this is not required. As discussed above, third and fourthNVIS filters and associated LEDs can also be used so that each edgeportion (or substantially the entire periphery) of the light guidecontains a NVIS filter and associated LEDs.

In this embodiment, a directing element 475 is placed above and alongthe second plurality of LEDs 455 to direct the light through the NVISfilter 465 and into the edge surface 434 of the light guide 430. Here,the reflective surface 476 of the directing element 475 connects roughlybetween the mounting structure 25 and the light emitting surface 432 ofthe light guide 430. In this particular embodiment, the reflectivesurface 476 of the directing element 475 is curved, but this could alsobe a sloped or slanted, relatively straight line. A separating element490 is preferably placed between the first plurality of LEDs 420 and thesecond plurality of LEDs 455. Here, the separating element 490 is placedbelow the NVIS filter 465. The separating element 490 may be reflectiveor absorptive and is preferably placed and chosen to prevent light fromthe second plurality of LEDs 455 from entering the light guide 430without passing through the NVIS filter 465.

In this particular embodiment, the separating element 490 is comprisedof separating sub-elements 491 and 492 with the NVIS filter 465 placedin between the two sub-elements 491 and 492. By using sub-elements,there can be two different properties associated with the overallseparating element 490 once assembled. For example, separatingsub-element 491 may have light absorbing properties while separatingsub-element 492 may have light reflecting properties. Alternatively,separating sub-element 491 may have light reflecting properties whileseparating sub-element 492 may have light absorbing properties. Stillfurther, both sub-elements may be reflective or absorbing or anycombination in between.

As discussed above, the various LCD components 480 can vary widely arenot specific to the various exemplary embodiments herein.

For the embodiments which utilize the ‘saw-tooth’ type of profile forthe light collecting surface, the vertical sub-surfaces may bereflective over the majority of the surface but transmissive in theareas directly adjacent to the LEDs. Further, in some embodiments theedge surfaces which are adjacent to the NVIS filter may be reflectiveover the majority of the surface but transmissive in the areas directlyadjacent to the LEDs. The vertical sub-surfaces, slanted sub-surfaces,edge surfaces, and light collecting surface may be smooth,textured/embossed, partially or wholly reflective, or any combination ofthese.

The light guide used with the various embodiments can have internalproperties which are tailored to the specific application. By way ofexample and not by way of limitation, the internal properties of thelight guide may be: optically clear, translucent, having lightscattering particles, embedded features (ex. reflective wires, wiremeshes, discrete reflectors/diffusing elements), or any combination ofthese.

As used herein, an NVIS filter is any device which is capable ofremoving or reducing wavelengths (typically longer than ˜650 nm) ofelectromagnetic radiation which may disrupt the NVIS components. In someembodiments, the NVIS filter may be a hot mirror that substantiallyreflects wavelengths longer than ˜650 nm. In other embodiments the NVISfilter may be a film or substrate which substantially absorbswavelengths longer than ˜650 nm. The NVIS filters may be a singular‘strip’ of material which covers the edge surface of the light guidewhich is adjacent to the night-mode LEDs. Alternatively, the NVISfilters may comprise several strips or discrete pieces of material whichare placed adjacent to one another.

Although some of the embodiments shown with a landscape-typeorientation, the exemplary embodiments of the backlight device taughtherein can be used with any orientation of LCDs (landscape, portrait,square, or any other shape/orientation). However, if a landscapeorientation is being used, it is preferable to place the second or thirdplurality of LEDs along the longer edge of the display to achieve thebest luminance uniformity and power density. It is also preferable touse a large number of low-power LEDs in order to increase the luminanceuniformity and efficiency of the backlight device.

The light guide 30 may be constructed out of a variety of materials.Typically, the base material for a light guide is a transparent orsemi-transparent plastic or glass. A variety of techniques can beapplied to the base material to produce the light scattering effectsdiscussed herein. A light scattering surface may have texture appliedthrough a number of processes including but not limited to: sanding,abrasion, laser etching, sand blasting, and acid etching. If producing alight guide by injecting liquid or molten material into a mold, thesurface textures may be present within the mold cavities. Alternatively,or in addition to the surface texture, particulate may be deposited onone or more surfaces of the light guide. Still further, patterns may beprinted onto one or more surfaces of the light guide using ink jet,screen printing, laser, or other printing techniques.

The LEDs may comprise a plurality of ‘white’ LEDs or may comprise acombination of non-white LEDs which, when combined together, producewhite light. One possible combination would be red, green, and blueLEDs. Some embodiments may contain other arrangements as any number ofdifferent LED arrangements can be practiced with the embodiments herein.

It should be noted that for the sake of explanation and clarity thevarious figures may not be drawn to scale. Specifically, as many LCDlayers are extremely thin, some portions have been enlarged orsimplified for explanatory purposes. The relative size and spacing ofthe LEDs may be enlarged for clarity purposes.

While certain embodiments of the present invention are described indetail above, the scope of the invention is not to be considered limitedby such disclosure, and modifications are possible without departingfrom the spirit of the invention as evidenced by the following claims:

What is claimed is:
 1. An electronic display assembly comprising: a liquid crystal layer; a substantially planar light guide positioned behind the liquid crystal layer and comprising: a light emission surface; a light-collecting portion opposing the light emission surface; four edge portions defining a periphery of the planar light guide; a first plurality of LEDs positioned within a first plane in a direct-lit orientation and arranged to direct the emitted light from the first plurality of LEDs into the light-collecting portion; a first NVIS filter placed adjacent to the light guide; and a second plurality of LEDs positioned within the first plane and near an edge portion, arranged to direct the emitted light from the second plurality of LEDs through the NVIS filter and into the light guide.
 2. The electronic display assembly of claim 1 further comprising: a second NVIS filter placed adjacent to the light guide; and a third plurality of LEDs positioned within the first plane and near an edge portion opposite the edge portion containing the second plurality of LEDs, and arranged to direct the emitted light from the third plurality of LEDs through the second NVIS filter and into the light guide.
 3. The electronic display assembly of claim 1 further comprising: a directing element placed adjacent to the second plurality of LEDs which directs the emitted light from the second plurality of LEDs through the first NVIS filter and into the light guide.
 4. The electronic display assembly of claim 1 further comprising: a mounting structure attached to both the first and second plurality of LEDs.
 5. The electronic display assembly of claim 1 further comprising: light scattering features within the light guide.
 6. An electronic display assembly comprising: a liquid crystal layer; a substantially planar light guide placed behind the liquid crystal layer and comprising: a light emission surface; a light-collecting surface opposing the light emission surface; four edge surfaces defining a periphery of the planar light guide; a mounting structure placed adjacent to the light-collecting surface and substantially parallel to the planar light guide; a first plurality of LEDs placed on the mounting structure to direct the emitted light from the first plurality of LEDs vertically into the light-collecting portion; a NVIS filter placed adjacent to one of the edge portions; and a second plurality of LEDs placed on the mounting structure and near the NVIS filter so that the emitted light from the second plurality of LEDs passes through the NVIS filter, and into the edge portion of the light guide.
 7. The electronic display assembly of claim 6 further comprising: a directing element placed adjacent to the NVIS filter.
 8. The electronic display assembly of claim 6 further comprising: a directing element placed between the second plurality of LEDs and the NVIS filter.
 9. The electronic display assembly of claim 6 further comprising: a directing element placed so that light from the second plurality of LEDs reflects off the directing element before passing through the NVIS filter.
 10. An electronic display assembly comprising: a liquid crystal layer; a substantially planar light guide placed behind the liquid crystal layer and comprising: a light emission surface; a light-collecting portion opposing the light emission surface; four edge portions defining a periphery of the planar light guide; a first plurality of LEDs arranged to direct the emitted light from the first plurality of LEDs into the light-collecting portion; a first NVIS filter placed adjacent to one of the edge portions; and a second plurality of LEDs arranged to direct the emitted light from the second plurality of LEDs through the NVIS filter and into an edge portion; where the first and second plurality of LEDs are arranged such that the axis of the strongest portions of emitted light are substantially parallel to one another.
 11. The electronic display assembly of claim 1 further comprising: a second NVIS filter placed adjacent to the edge portion opposite the edge portion containing the first NVIS filter; and a third plurality of LEDs arranged to direct the emitted light from the third plurality of LEDs through the second NVIS filter and into the edge portion.
 12. The electronic display assembly of claim 11 further comprising: a directing element placed adjacent to the second plurality of LEDs which directs the emitted light from the second plurality of LEDs through the first NVIS filter and into the light guide.
 13. The electronic display assembly of claim 11 further comprising: a mounting structure attached to both the first and second plurality of LEDs.
 14. The electronic display assembly of claim 11 further comprising: light scattering features within the light guide.
 15. An electronic display assembly comprising: a liquid crystal panel; a substantially planar light guide positioned behind the liquid crystal panel and comprising: a light emission surface; and a light-collecting surface opposing the light emission surface; and four edge portions defining a periphery of the light guide; a mounting structure placed adjacent to the light-collecting surface and substantially parallel to the planar light guide; a first plurality of LEDs placed on the mounting structure to direct the emitted light from the first plurality of LEDs into the light-collecting portion; a NVIS filter placed adjacent to one of the edge portions and oriented substantially perpendicular to the mounting structure; and a second plurality of LEDs placed on the mounting structure so that the emitted light from the second plurality of LEDs passes through the NVIS filter.
 16. The electronic display assembly of claim 15 further comprising: a directing element placed adjacent to the NVIS filter.
 17. The electronic display assembly of claim 15 further comprising: a directing element placed between the second plurality of LEDs and the NVIS filter.
 18. The electronic display assembly of claim 15 further comprising: a directing element placed so that light from the second plurality of LEDs reflects off the directing element before passing through the NVIS filter.
 19. The electronic display assembly of claim 15 further comprising: light scattering features within the light guide.
 20. The electronic display assembly of claim 15 wherein: the first and second plurality of LEDs are oriented so as to emit the strongest light in a direction parallel to each other. 